NASA - National Aeronautics and Space Administration

It's the little things that matter.

On every space shuttle flight, the primary mission objectives attract the most attention. On Space Shuttle Endeavour's next flight, STS-118, these include the delivery of the International Space Station's S5 truss segment. The S5 will extend the station's truss, or backbone, making it possible to install additional solar arrays in the future. Also capturing public attention this mission is the first flight of an Educator Astronaut, mission specialist Barbara Morgan.



Image above: A technician prepares a Control Moment Gyroscope for delivery to the space station. The STS-118 astronauts will make repairs to the gyro system. Credit: NASA.

In addition to Morgan, the crew will consist of commander Scott Kelly, pilot Charles Hobaugh, and mission specialists Tracy Caldwell, Rick Mastracchio, Alvin Drew and Dave Williams.

For any mission to be successful, several other lesser-known factors come into play. The public may not hear as much about power transfer systems or control moment gyroscopes, but those elements are very important to the mission and station's operation. Several of these other elements will play big roles on STS-118, which is a 14-day mission currently scheduled for August 8, 2007.

One of those other elements is that the flight will be the first to use a new Station-to-Shuttle Power Transfer System. Electrical power is one of the factors that limit the length of a space shuttle flight. The SSPTS will make it possible to supplement the shuttle's fuel cells with power from the space station's solar arrays.

If the system works as planned, Endeavour will stay docked at the space station two days longer than would previously have been possible. The extra time will let the shuttle and space station crews perform additional tasks, including a fourth spacewalk, and potentially get further ahead of schedule on station assembly. The new system also shows how much the space station has "grown up" since it was first launched. On early shuttle visits, the orbiter would transfer power to the station. With the addition of new station solar arrays and this new system, the space station is now the spacecraft with power to spare.


Image above: The Canadarm2 was used to install the P3/P4 truss segment during the STS-115 mission. Credit: NASA.

Another task of the mission is to repair the station's Control Moment Gyro system. The station has four of these gyroscopes, which are used to control its orientation in space. One of the gyros was powered down in October 2006 when it began vibrating excessively. The STS-118 crew will replace the failed gyro. While only two gyros are needed for proper orientation, the repair will restore redundancy to prevent problems from occurring in the future.

Another important part of space station assembly that sometimes does not receive much recognition is the use of the two robotic arms, the shuttle's Canadarm and the station's larger Canadarm2. The arms work together to install new station elements.

On a typical mission, the Canadarm might be used to lift a massive station element out of the space shuttle cargo bay. The shuttle's robotic arm would then hand the part to the Canadarm2, which would move the piece into place for installation. The arms can also be used during spacewalks to move astronauts to locations needed to carry out assembly work.

While the spacewalking crewmembers are often the ones in the limelight for the challenging work they do installing new components, they couldn't do their job without the help of the robotic arms and the astronauts who operate them.

With the shuttle crew working to help complete the space station by 2010, the public will hear about exciting things going on in orbit. But behind-the-scenes, a lot of elements must work together to make it all happen.

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David Hitt/NASA Educational Technology Services